Field of the Invention
This invention relates to a process for the conversion of a gaseous paraffinic feed containing a major proportion of C.sub.2 to C.sub.12 aliphatic hydrocarbons to aromatics in the presence of a crystalline zeolite catalyst containing an added metal consisting essentially of zinc.
Zeolites and alumina have been used in the past in the preparation of catalysts for the production of aromatic hydrocarbons from aliphatic hydrocarbons. The aliphatic hydrocarbon is passed over the catalyst at an elevated temperature in the liquid or vapor phase. Zeolites of various types have been suggested for the preparation of such catalysts. Examples of such zeolites are mordenite and the ZSM varieties, some of which contain zinc as ions which have been impregnated on the zeolite substrate or for which the original cations have been exchanged. However, it has sometimes been considered desirable to improve the yields of aromatic hydrocarbons when using such catalysts.
U.S. Pat. No. 4,097,367 teaches the catalytic conversion of olefinic naphthas which contain diolefins over a special catalyst to yield a product stream which contains little or no non-aromatics boiling in the range of benzene, toluene and xylene. The catalyst is a combination of zinc and a metal from Groups IB and VIII of the Periodic Table with a crystalline aluminosilicate zeolite having a silica-alumina ratio greater than 12 and a Constraint Index not less than one nor greater than 12.
U.S. Pat. No. 4,120,910 discloses that aromatic compounds can be produced by contacting, in the absence of added air or oxygen under suitable conversion conditions, a gaseous, paraffinic feed stock containing a high percentage of ethane with a ZSM-5 type crystalline aluminosilicate zeolite catalyst having incorporated therein a minor amount of a metal or metal oxide from Group VIII, IIB, or IB of the Periodic Table. Especially preferred is a zinc-copper mixture.
U.S. Pat. No. 4,350,835 teaches a catalytic process for converting a feedstock comprising a high percentage of ethane to aromatics employing as a catalyst a zeolite with a silica-alumina ratio of at least 12 and having incorporated therein a minor amount of gallium. The patent also discloses, for comparison purposes a catalyst containing 1% zinc and 0.25% copper supported on a ZSM-5 zeolite having a silica to alumina ratio of 40.
U.S. Pat. No. 4,392, 989 shows the aromatization of paraffin feeds containing C.sub.2 -C.sub.12 hydrocarbons using a catalyst comprising a zeolite containing zinc in combination with gallium or palladium.